More specifically, this invention applies generally to the technical field encompassing equipment used to feed infusion products to a packaging machine which fills into respective filter bags predetermined charges of non-homogeneous material consisting, for example, of flowers whole leaves, herbs or fruits and mixtures thereof, without limiting the scope of the invention.
This material is extremely fragile and is composed of elements whose physical properties, such as shape, specific weight, and size, differ widely from each other.
There are various ways of preparing the charges after the material has been mixed according to specific recipes. The charges may be made, for example, using weighing systems which guarantee that each charge has a predetermined weight or with volumetric systems which define, for each charge, a predetermined quantity of material, as described in patent EP584213 to Bonomelli s.r.l.
Patent EP584213 describes a volumetric batcher of the drawer type (plate) designed to batch whole chamomile flowers. The batcher is located downstream of a container into which the whole chamomile flowers are conveyed by a conveyor belt until the container is full to a predetermined level. More specifically, at the bottom of the container, there is a screw feeder mounted in a substantially horizontal manner and fully immersed in the chamomile flowers. The screw feeder is driven by an independent motor and conveys the chamomile flowers through a horizontal conduit towards a vertical conduit which communicates with the selfsame horizontal conduit.
The vertical conduit feeds a batching chamber of the drawer type batcher by means of a pad which operates longitudinally inside the vertical conduit.
The drawer type batcher is made up of three plates mounted one above the other: an upper plate and a lower plate, which are both fixed, and a movable plate located between the two fixed plates. In particular, the batching chamber is formed in the movable plate. Thus, the upper plate acts as a levelling device to form the right charge of material in the batching chamber and, together with the lower plate, acts as a charge containment plate which prevents material from falling out. The batching chamber is thus filled with chamomile flowers through the upper plate by means of a first hole which is coaxial with the vertical conduit and in which the pad operates. When the batching chamber is completely full, the movable plate moves axially and places the chamber in communication with second holes, which are coaxial with each other and which are formed in both the upper and lower, fixed plates. Next, a piston which slides through the second holes expels the charge of material from the batching chamber and directs it to a packaging machine which in the meantime has prepared the bags of filter material adapted to receive the charges.
In this solution, the chamomile flowers are compressed to a varying extent both inside the horizontal conduit, by the action of the screw feeder which conveys the flowers towards the vertical conduit, and inside the vertical conduit itself, by the action of the pad.
Another prior art solution for making charges of loose material and feeding them onto a web of filter material used for making filter bags comprises a cylindrical metering device with a horizontal axis of rotation and a plurality of radial cavities giving onto the outer cylindrical surface. The drum is interposed between a feed hopper for the loose material to be metered and the web of filter material onto which the metered charges to be packaged are placed.
In particular, the hopper for the loose material has an outlet opening which faces the metering drum and which is delimited, on one side, by a containment wall and, on the other side, by a levelling device.
In this solution, there are pistons sliding in the radial cavities which define the metering chambers in the drum. The pistons are driven by the continuous rotation of the drum and are made to move radially, through the agency of cam means, between a maximum distance from the periphery of the metering drum, defining the bottom dead centre, and a minimum distance from the periphery of the metering drum, defining the top dead centre. At the bottom dead centre, the piston is inserted gradually under the feed hopper on the containment wall side, allowing the loose material into the metering chamber. The continuous rotation of the drum causes the piston to move to the top dead centre while facing the outlet opening of the hopper and where, under the action of the levelling device, the charge of loose material is formed. As long as the piston remains at the top dead centre, the charge formed is held within the metering chamber by a stop member located downstream of the levelling device. As the stop member moves away, the charge formed is discharged from the metering chamber and placed on a horizontal stretch of the web of filter material substantially tangent to the metering drum. At the same time, the piston starts moving back to the bottom dead centre, which it reaches before being inserted into the zone where the loose material is drawn from under the hopper.
The devices described above, also called volumetric metering devices, have several disadvantages, connected with the levelling operation, during which the loose material being metered is subjected to a cutting-like action which damages it and deteriorates its quality. Moreover, these devices exert a compressive action on the material, which is not a problem if the material is homogeneous in nature. In the case of non-homogeneous material, however, where the individual elements must remain whole, compression damages parts of the material and deteriorates its quality.
The wholeness of the infusion material is an essential factor in guaranteeing the quality of the product for the consumer and it is therefore necessary to preserve the wholeness as far as possible.